Impact of Organic Cation Length on Photoluminescence and Crystal Structure for Zero-Dimensional Organic Copper Halides Containing [Cu₄Br₈]⁴– Clusters

Low-dimensional (LD) organic metal halides (OMHs) composed of organic cations and metal halide networks have been extensively investigated due to their excellent photophysical properties. The effect of organic cations on the electronic structure of the LD-OMHs was investigated by reacting CuBr with 1,4-diazabicyclo[2.2.2]octane salts having different alkyl chain lengths, leading to the formation of two new 0D-OMHs with similar structures containing a rare [Cu4Br8]4- clusters. The only structural difference observed in the metal halide networks was the spacing of the metallic clusters due to the length of the alkyl chains. Such a difference significantly impacts the emission and photoluminescence quantum yields (ΦF = 98% vs 51%), exhibiting long emission decay times of 79.7 μs (1) and 72.6 μs (2), respectively. Photophysical properties and crystal structure analysis clearly reveal that the alkyl chain length of organic cations affects the electric field around the inorganic cluster, leading to the distortion of the inorganic clusters and resulting in the emission intensities, wavelengths, and band broadnesses.